1. Field of the Invention
The present invention relates to a method for simulating an impurity diffusion in a semiconductor while the semiconductor is being oxidized.
2. Description of the Related Art
In a prior art method for simulating a concentration of impurities within a silicon material while the silicon material is being oxidized, an initial triangular mesh configuration is set in a semiconductor device. Particularly, a trench structure can be accurately represented by the triangular mesh configuration (see: C. S. Rafferty et al., "Iteractive Methods in Semiconductor Device Simulation", IEEE Transactions on Electron Devices, Vol. ED-32, No. 10, pp. 2018-2027, October 1985). Also, a control volume is set in each mesh point (grid). In this case, a closed surface of the control volume is defined by circumcenters. One of the circumcenters is a center of a circle that is circumscribed about a triangle formed by three grids. Further, initial impurity concentrations are set for the control volumes.
Next, the semiconductor device, i.e., the triangle mesh configuration is deformed by assuming an execution of an oxidation process thereupon. Concretely, the locations of the grids are changed, and the control volumes thereof are also deformed.
Next, the impurity concentrations of the deformed control volumes are changed. For example, if the deformed control volume is increased, its impurity concentration is diluted. Contrary to this, if the deformed control volume is decreased, its impurity concentration is enriched.
Next, it is determined whether or not the deformed mesh configuration satisfies Delaunay's division, which will be explained later in detail. Only when the deformed mesh configuration does not satisfy Delaunay's division, is a new mesh configuration satisfying Delaunay's division arranged, and also appropriate impurity concentrations are given to new grids.
Next, impurity concentrations for the grids of the deformed or rearranged mesh configuration are calculated by an impurity diffusion equation.
The prior art impurity diffusion simulation method will be explained later in detail.
In the above-mentioned prior art impurity diffusion simulation method, however, after the new mesh configuration is arranged, the control volumes are also changed. Therefore, since the impurity concentrations of the grids are not changed even when the control volumes are changed by the arrangement of the mesh configuration, the total amount of impurities is not preserved between the deformed mesh configuration and the non-deformed mesh configuration. This makes the impurity concentrations inaccurate.